It is now common practice to fill catalytic reactor vessels having fixed catalyst beds using a catalyst distributor. Such technique has become known as catalyst oriented packing (frequently referred to as COP loading) of vessels. The primary purpose is to minimize void spaces and consequently local "hot spots" which can occur during exothermic reactions of hydrocarbons with the catalyst particles. Additionally, it increases the bulk density of the solid particulate material, catalyst particles, which in turn improves the throughput of reactants for a given size of vessel. Further, it limits settling of the bed when the reactor is brought on stream due to hydraulic forces of fluid flow in the reactor. In general, catalysts can be loaded in 10 to 15% less reactor volume and increased contacting efficiency permits operation of the reactor at lower reactor temperatures.
In general, previously known catalyst oriented loading apparatus included a single distributor disc either having a plurality of radial blades or fin members on top of the rotating element. In general the distributor is a cone shaped member and must be driven at different speeds to achieve a form of radial distribution of catalyst particles falling on the distributor disc. The disc flings or casts the particles toward the side walls of the reactor vessel at distances relate to disc speed. Alternatively, the disc may be a flat plate having vanes formed thereon and having a few holes formed in the plate to permit some of the catalyst particles to fall directly downwardly from the rotating member into the center of the reactor vessel.
U.S. Pat. No. 3,804,273 Uhl is directed to apparatus for loading a catalyst bed with a radial distributor having a conical surface. The only method of distributing catalyst across a large diameter bed is to increase and decrease the speed of the rotating disc.
U.S. Pat. No. 3,972,686 Johnson et al, discloses a flat disc having vanes and a plurality of slots or holes through which some of the catalyst may fall near the center of the bed; the remainder of the catalyst is thrown toward the side. This system also requires variation in the speed of the rotating disc to cover the entire level of a catalyst reactor bed.
A particular disadvantage of both of the prior arrangements lies in the fact that the catayst is thrown into a circular or annular mound which tends to classify catalyst particles falling on it. The larger particles roll to the bottom and outside of the mound while the smaller particles stop on the mound itself. While to a certain extent, these difficulties are alleviated by varying the speed of the rotating disc, the interior of such a bed is usually too full of dust to permit the operator to actually see the catalyst bed from the top while the loader is operating. Accordingly, it is necessary to determine the probable level of distribution by the number of drums of catalyst that have been loaded at a given bed level. Such a procedure is time consuming and not necessarily accurate to the point of permitting level filling of the bed. In fact, it is generally the practice to fill the bed at the outer edge higher than necessary say 6 to 12 inches and then alternately increase the height of the center level above that at the outer edge by a similar amount, and so forth, up the reactor as the depth of the bed or beds is increased throughout the reactor.